Vertex Pharmaceuticals Inc. said Thursday that final data from a midstage clinical study of an experimental combination of its cystic fibrosis drugs “showed statistically significant improvements” in lung function among some adults with cystic fibrosis.

In early May, Cambridge-based Vertex issued an “interim analysis” on the effects of its Kalydeco therapy used in combination with the experiemental drug VX-809. Kalydeco is the first drug that seeks to target the underlying cause of cystic fibrosis, a rare and often fatal genetic disease. The company’s stock shares surged on the news.

A few weeks later, Vertex revised the interim analysis, saying it overstated the clinical data. Between the initial report and the revision, several executives and company directors sold stock shares worth millions of dollars.

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A Vertex spokesman said Thursday that today’s final results from the study confirm what the company said in late May’s revised report --- that the combination of Kalydeco and VX-809 showed statistically significant improvements in lung function among adults with cystic fibrosis who have two copies of the F508del mutation.

At around 1:30 p.m. Thursday, Vertex shares were trading at $52.93, down $8.18, or about 13.3 percent.

A Vertex press release issued Thursday included a statement from Chris Wright, M.D., the company’s senior vice president of global medicines development and medical affairs.

“We are focused on developing additional medicines to treat the underlying cause of cystic fibrosis, and these data represent exciting progress toward that goal,” Wright said. “The data announced today show that the addition of Kalydeco to VX-809 resulted in improvements in lung function and support our plans to start a pivotal program in people with cystic fibrosis who have two copies of the most common CFTR mutation in early 2013.”